Flash lamp system

ABSTRACT

A flash tube has an internal gas pressure above 600 millimeters of mercury. It is energized by a capacitor having an operating voltage such that the ratio of the discharge gap of the tube to said operating voltage is no greater than 0.5 centimeters per 100 volts and having a capacitance such that the voltage will not drop by more than 15 percent upon reaching peak current through the tube. In one embodiment the tube has two electrode chambers connected by a duct and the chambers, but not the duct, are cooled. In a second embodiment there are two radiators, one for ultraviolet radiation and the other for infrared radiation. In one form these two radiators are flash tubes operated in a timed manner so that the maximum of the infrared radiation from one coincides with the maximum of the ultraviolet radiation from the other.

United States Patent Ludloff 1 Jan. 14, 1975 [5 FLASH LAMP SYSTEM 2.924.731 2/1960 Martt ct a1 313 1114 x 3.148.307 9/1964 Edgerton et a1. 315/237 [75] Inventor- Wolfgimg Ludloffl porzwesthovem 3,453,427 7/1969 Leiga @1111. 315 241 x Germany [73] Assignee; Multiblitz Dr -lng I), A, Primary Examiner-Rudolph V. Rolinec Mannesman GmbH & Co. KG, Assistant ExaminerE. R. LaRochc Porz-Westhoven, Germany Attorney, Agent, or FirmDarbo, Robertson & 22 Filed: May 3, 1973 Vandenburgh [21] Appl. No.: 357,001 [57] ABSTRACT A flash tube has an internal gas pressure above 600 [30] Foreign Application Priority Data millimeters of mercury. It is energized by a capacitor May 6, 1972 Germany 2222365 having an Operating Voltage Such that the ratio of the discharge gap of the tube to said operating voltage is 52 us. 121 .1 315/178, 250/495, 313/43, no greater than centimeters P 100 volts and 313/220 313/221 315/113, 315/232 ing a capacitance such that the voltage will not drop 315/241 R, 315/324 by more than 15 percent upon reaching peak current 511 1111. c1. 11011 61/30, H05b 41/14 through the In one embodiment the tube has two 581 Field 01 Search 313/42, 43, 184, 185, 214, electrode Chambers connected by a duct and the 313/220; 315/112, 113 178! 179 132 232, chambers, but not the duct, are cooled. In a second 1 R, 241 S, 323, 324, 325; 250/493, 494, bodiment there are two radiators, one for ultravio- 495, 504 let radiation and the other for infrared radiation. In one form these two radiators are flash tubes operated 5 References Cited in a timed manner so that the maximum of the infra- UNITED STATES PATENTS red radiation from one coincides with the maximum of the ultraviolet radiation from the other. 1,646,010 10/1927 Clover 250/495 X 2,919,369 12/1959 Edgerton 313/185 13 Clalms. 3 aw g gures FATENYEU 3860.853

sum 0? a FIG. 1

FATENTED $860,853

SHEEI 3 OF 3 FIG. 3

FLASH LAMP SYSTEM BACKGROUND AND SUMMARY OF THE INVENTION My earlier patent application Ser. No. 247,318, now US. Pat. No. 3,800,187, flled Apr. 25, 1972, relates to a flash lamp system for producing high-intensity shortwave radiation flashes by using an electronic flash tube which is ignited by means of an ignition electrode and thereupon a storage capacitor discharges through the flash tube. According to the basic idea of that application, the flash tube is operated with a discharge circuit resistance which is so low that the peak current of the discharge is defined substantially only by the flash tube. According to a further feature of that application, the flash tube is constructed of material which is permeable to ultraviolet light and comprises a discharge duct and a dead space outside the discharge duct, the volume of the said dead space being at least equal to the volume of the discharge duct. One system according to the application is utilized in conjunction with photo-initiation of drying processes or curing processes, for example of varnishes or printers inks. In this connection, it is essential to produce current peaks which are as high as possible in the flash tube so that short but high-intensity short-wave (ultraviolet) radiation flashes are produced.

The principal object of the present invention is to provide a flash lamp system according to said application so as to produce an optimum drying effect.

The invention is based on the knowledge that to achieve an optimum drying effect, it is essential for the peak current of the flash discharge to be as high as possible and for the current rise to its peak value to be as steep as possible. The drying time T, which is a measure of the achieved drying effect, varies approximately inversely proportionally to the square of the peak current T (Ill) The total energy of the flash discharge is therefore of secondary significance for the drying effect. Accordingly, the capacitance of the storage capacitor is made only sufficiently large to ensure that the current rise at the beginning of the discharge is not decelerated by the capacitor voltage reduction due to the discharge. The operating voltage should be made as high as possible unless disproportionately large insulation problems occur. The internal resistance of the tube during discharge should be made as small as possible. The internal resistance of the tube defines the required capacitance of the capacitor with the condition that the capacitor voltage reduction at the discharge should be small. The high voltage and the demand for a small internal resistance of the tube in turn call for a gas pres sure which is high by comparison to conventional flash tubes in order to avoid the firing of the tube without a firing pulse. A relatively long flash tube would be desirable for geometrical reasons in view of the application of the system to varnish drying. However, this requirement is partially in contradiction to the demand for a high peak current.

By taking into account the preceding remarks the system according to the invention is constructed so that given a charging pressure above 600 mm.I-IG (millimeters of mercury) the ratio of the length of the discharge gap to operating voltage is smaller than or equal to 0.5 cm/lOO V and that the capacitance of the storage capacitor is so dimensioned that the capacitor voltage has not dropped by more than 15 percent upon reaching the peak current after the flash tube is fired.

It is advantageous if the capacitor is so dimensioned that the overall discharge time does not exceed 40 micro seconds.

Preferred dimensions include a discharge gap of approximately l5 cm, an operating voltage of approximately 3,200 V and a capacitance of the storage capacitor of approximately 4 pf.

It has also been found that the drying effect of known flash tubes is impaired because the material of the flash tube envelope absorbs a substantial proportion of the generated ultraviolet (UV) radiation. In conventional flash tubes constructed from quartz this is due to an aging effect in the course of which the flash tubes acquire a blue coloring.

In a further embodiment of the invention, the flash tube is therefore constructed of synthetic quartz glass of high, i.e., about percent transmissivity for ultraviolet and infrared radiation. For example, such material is sold by Heraeus Schott Quarzschmelze GmbH., of Hanau, West Germany, under the name of Suprasil (trademark).

According to the prior art, endeavors are always based on the assumption that it is important to generate an ultraviolet flash while avoiding heat and infrared radiation. Investigations have shown that this assumption does not apply but instead the drying effect can be substantially improved by using ultraviolet flashes in conjunction with simultaneous infrared action. It should be noted that this improvement is achieved neither by the action of infrared radiation alone nor by infrared radiation and ultraviolet flashes applied separately in terms of time.

In a further embodiment of the invention an infrared radiator is therefore provided in addition to the flash tube. The intensity of the infrared radiator may be advantageously variable for the optimum adjustment of its intensity.

In another solution of the problem a second electronic flash tube adapted to emit infrared radiation is provided, the discharge current of which fires, after a given delay, the flash tube for emitting ultraviolet radiation so that the emission maximums of the infrared radiation or the ultraviolet radiation respectively of the two tubes coincide with respect to time. This solution to the problem is based on the experimentally discovered fact that the maximums of ultraviolet radiation and infrared radiation of a flash tube are staggered with respect to time.

Another feature is that the flash tube has expande electrode chambers and a cooling device which acts only on the electrode chambers. This causes the discharge gap between the electrode chambers to be heated to a glowing temperature and achieves two advantageous results, namely: (1) The envelope of the flash tube itself thus emits infrared radiation which, as already mentioned, improves the drying effect when ultraviolet flashes are simultaneously applied. (2) Heating the envelope to a red heat also counteracts any change of the absorption characteristic due to aging, even in ordinary quartz, which would otherwise impair the transmissivity for ultraviolet radiation as already described.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a first embodiment of a flash tube system according to the invention and used for varnish drying or curing;

FIG. 2 is a schematic wiring diagram of a second embodiment; and

FIG. 3 is a diagrammatic perspective view of a third embodiment used for the simultaneous treatment with ultraviolet and infrared radiation.

DESCRIPTION OF SPECIFIC EMBODIMENTS The following disclosure is offered for public dissemination in return for the grant of a patent. Although it is detailed to ensure adequacy and aid understanding, this is not intended to prejudice that purpose of a patent which is to cover each new inventive concept therein no matter how others may later disguise it by variations in form or additions or further improvements.

In the embodiment of FIG. 1 there is a flash tube the envelope of which is quartz glass. This tube has a straight discharge duct or chamber 12 with electrode chambers 14 and 16 extending at right angles to the duct at the ends thereof. Each of the electrode chambers has a volume which is at least equal to that of the discharge duct 12. Electrodes l8 and 20 are positioned in the respective electrode chambers 14 and 16. The flash tube 10 is connected in a conventional flash lamp circuit and is fired by a firing electrode which is not illustrated in FIG. 1.

The flash tube 10 is so dimensioned that the ratio of discharge gap to operating voltage is smaller than or equal to 0.5 cm/ 100 V. In a preferred embodiment, the discharge duct 12 incorporates a discharge gap of approximately cm in length. The operating voltage to which the storage capacitor is charged amounts to 3,200 V. To prevent self-discharge of the flash tube 10 without a firing pulse being supplied to the firing electrode, the charging pressure of the tube is made greater than 600 mm Hg. The capacitance of the storage capacitor is 4 pf. This provides peak currents of approximately 750 A.

The flash tube 10 is mounted in a reflector 22 whose exterior is provided with a trough-shaped cooling air duct 24 through which a stream of cooling air is conducted by means of a blower (not shown) as indicated by the arrows. The electrode chambers 14 and 16 of the flash tube 10 extend into the cooling air duct 24 while the discharge duct 12 is positioned in the reflector 22 where it is not cooled by the air flow through duct 24.

As a result of the high loading during operation, the envelope of the flash tube 10 is substantially heated in the zone of the discharge duct 12 so that the envelope emits infrared radiation. That infrared radiation in conjunction with the ultraviolet flashes which are simultaneously produced, assists the drying effect as already mentioned. Heating also prevents a change of the absorption characteristics of the quartz due to aging.

FIG. 2 shows a circuit in which ultraviolet flashes and infrared flashes are simultaneously produced by using two flash tubes 26 and 28. The embodiment of FIG. 2

is based on the experimentally found knowledge that a 6 flash tube emits ultraviolet radiation as well as infrared radiation but in the course of the discharge, the maximums of infrared radiation and ultraviolet radiation are staggered with respect to time.

In this circuit the flash tube 26 is initially fired and the infrared radiation therefrom is utilized. The discharge current of flash tube 26 fires a second flash tube 28 after a delay which delay is such that the maximum of the ultraviolet radiation of the flash tube 28 coincides with the maximum of the infrared radiation of the flash tube 26.

The flash tube 26 is connected to a supply storage capacitor 30. It is fired by means of a firing electrode 32 to which a firing pulse is applied. This firing pulse is generated in the usual manner by the discharge of a firing capacitor 36 through a firing transformer 38 when a firing contact (switch) 34 is closed. The firing capacitor is charged by the operating voltage of 3,200 V applied across a voltage divider comprising the resistors 40 and 42. The primary winding of a transformer 44 is connected in the discharge circuit of the storage capacitor 30 and the flash tube 26. The pulse which occurs in the transformer secondary when the flash tube 26 is discharged through the primary charges a capacitor 48 via a diode 46. When this capacitor 48 has been charged to a sufficient voltage, which requires a given amount of delay, that voltage fires a thyristor 50. This conductance of thyristor 50 closes a circuit from a firing capacitor 52 and through the primary winding of a firing transformer 54. The resulting current flow through the primary produces a firing pulse in the secondary which pulse is applied to a firing electrode 56 of the flash tube 28. Thereupon a supply storage capacitor 58 discharges via the flash tube 28. This discharge occurs with the aforementioned given delay following the discharge of tube 26. The firing capacitor 52 is once again charged by the operating voltage of 3,200 V applied across a voltage divider comprising resistors 60 and 62.

In the embodiment of FIG. 3, a surface 64, for example a varnish surface which is to be dried, is illuminated with ultraviolet flashes from an ultraviolet flash tube which is positioned in a reflector 66 and is driven and controlled from a conventional current generator 68. This may comprise an arrangement of the kind shown in FIG. 1. The surface 64 is simultaneously irradiated by an infrared radiator 70 which is positioned in a re flector 72 and is fed from the mains (e.g., ordinary ac. power supply). The power of the infrared radiator 70 may be varied, for example by means of an adjustable series resistor 74.

I claim:

1. In a flash lamp apparatus comprising a flash tube filled with gas under pressure, a supply storage capacitor means, means to apply an operating voltage to said storage capacitor means, a discharge circuit including said flash tube and said supply capacitor means and having a resistance so low that the peak current of the discharge is defined substantially only by the flash tube, the improvement comprising:

said pressure of the gas in said tube being above 600 millimeters of mercury, said tube having a discharge gap of a length such that the ratio of said length to said operating voltage is no greater than 0.5 centimeters per lOO volts,

said capacitor means having a capacitance such that, after firing, the voltage thereof will not drop by more than 15 percent before reaching said peak current,

said flash tube being positioned to apply the radiation therefrom to a surface,

infrared radiator means positioned so that the radiation therefrom is also applied to said surface along with said radiation from said flash tube,

said radiator means comprising circuit means including a second flash tube, and means connecting said second circuit means to said first circuit means to fire the first mentioned flash tube a given period of time after said second flash tube, said given period of time being such that the maximums of the infrared radiation from said second flash tube coincides with the ultraviolet radiation from the first mentioned flash tube, and

means connected to said radiator means for varying the intensity of the infrared radiation.

2. In an apparatus as set forth in claim 1, wherein the characteristics of the capacitor means provides a total discharge time which does not exceed 40 micro seconds.

3. In an apparatus as set forth in claim 2, wherein the flash tube has a discharge gap of approximately centimeters, the capacitor means has a capacitance of about 4 microfarads, said means to apply said operating voltage provides an operating voltage of about 3,200 volts.

4. In an apparatus as set forth in claim 3, wherein said discharge tube includes envelope means having high transmissivity for ultraviolet and infrared radiation, said envelope means being formed of synthetic quartz glass.

5. In an apparatus as set forth in claim 4, wherein said envelope means defines two electrode chambers and a discharge duct connecting said chambers, and including cooling means for the chambers only.

6. In an apparatus as set forth in claim 1, wherein said discharge tube includes envelope means having high transmissivity for ultraviolet and infrared radiation, said envelope means being formed of synthetic quartz glass.

7. In an apparatus as set forth in claim 1, wherein said discharge tube includes envelope means, said envelope means defines two electrode chambers and a discharge duct connecting said chambers, and including cooling means for the chambers only.

8. In an electronic flash tube for generating light flashes having a high proportion of ultraviolet radiation, said tube comprising an envelope, main electrodes in the envelope between which electric current passes, a firing electrode, and a gas in said envelope which is excited to light emission by the passage of said current, said emission including ultraviolet light, the improvement comprising:

said envelope comprising a straight discharge duct and electrode chambers at the ends of the duct,

each of said electrode chambers having a volume which is at least equal to that of the discharge duct,

said main electrodes being positioned in the electrode chambers respectively and outside said duct in a manner permitting free communication of said gas between said duct and said electrode chambers,

said envelope having means for preventing any decrease of ultraviolet transmissivity of the envelope due to the effect of flash discharges through said duct.

9. In an electronic flash tube as defined in claim 8, wherein said preventing means comprises:

said electrode chambers extending at right angles to said discharge duct, an elongated reflector having a cooling air duct at the exterior thereof, said electronic flash tube being positioned with its discharge duct within the reflector and outside the cooling air duct and with said electrode chambers extending into said cooling air duct, and means for providing a cooling air stream through said cooling air duct, whereby in operation said envelope is substantially heated to prevent any change of ultraviolet transmissivity of the envelope.

10. In an electronic flash tube as defined in claim 8, wherein said preventing means comprises:

said envelope consisting of synthetic quartz glass.

11. In a flash lamp apparatus including a flash tube as set forth in claim 8, storage capacitor means for supplying said current, discharge circuit means including said storage capacitor means and said flash tube, and flash tube firing means connected to said firing electrode, the improvement comprising:

said discharge circuit means having a resistance so low that the peak current of the discharge is defined substantially only by the flash tube.

12. In an apparatus as set forth in claim 11 used to apply radiation to a surface, wherein said flash tube is positioned to apply the radiation therefrom to said surface, said apparatus including:

infrared radiator means positioned so that the radiation therefrom is also applied to said surface along with said radiation from said flash tube, said radiator means comprising second circuit means including a second flash tube, and means connecting said second circuit means to said firing means to fire the second flash tube a given period of time before said first mentioned flash tube is fired, said given period of time being such that the maximum of the infrared radiation from said second flash tube coincides with the ultraviolet radiation from the first mentioned flash tube.

13. In an apparatus as set forth in claim 12, wherein said preventing means comprises:

said envelope consisting of synthetic quartz glass. 

1. In a flash lamp apparatus comprising a flash tube filled with gas under pressure, a supply storage capacitor means, means to apply an operating voltage to said storage capacitor means, a discharge circuit including said flash tube and said supply capacitor means and having a resistance so low that the peak current of the discharge is defined substantially only by the flash tube, the improvement comprising: said pressure of the gas in said tube being above 600 millimeters of mercury, said tube having a discharge gap of a length such that the ratio of said length to said operating voltage is no greater than 0.5 centimeters per 100 volts, said capacitor means having a capacitance such that, after firing, the voltage thereof will not drop by more than 15 percent before reaching said peak current, said flash tube being positioned to apply the radiation therefrom to a surface, infrared radiator means positioned so that the radiation therefrom is also applied to said surface along with said radiation from said flash tube, said radiator means comprising circuit means including a second flash tube, and means connecting said second circuit means to said first circuit means to fire the first mentioned flash tube a given period of time after said second flash tube, said given period of time being such that the maximums of the infrared radiation from said second flash tube coincides with the ultraviolet radiation from the first mentioned flash tube, and means connected to said radiator means for varying the intensity of the infrared radiation.
 2. In an apparatus as set forth in claim 1, wherein the characteristics of the capacitor means provides a total discharge time which does not exceed 40 micro seconds.
 3. In an apparatus as set forth in claim 2, wherein the flash tube has a disCharge gap of approximately 15 centimeters, the capacitor means has a capacitance of about 4 microfarads, said means to apply said operating voltage provides an operating voltage of about 3,200 volts.
 4. In an apparatus as set forth in claim 3, wherein said discharge tube includes envelope means having high transmissivity for ultraviolet and infrared radiation, said envelope means being formed of synthetic quartz glass.
 5. In an apparatus as set forth in claim 4, wherein said envelope means defines two electrode chambers and a discharge duct connecting said chambers, and including cooling means for the chambers only.
 6. In an apparatus as set forth in claim 1, wherein said discharge tube includes envelope means having high transmissivity for ultraviolet and infrared radiation, said envelope means being formed of synthetic quartz glass.
 7. In an apparatus as set forth in claim 1, wherein said discharge tube includes envelope means, said envelope means defines two electrode chambers and a discharge duct connecting said chambers, and including cooling means for the chambers only.
 8. In an electronic flash tube for generating light flashes having a high proportion of ultraviolet radiation, said tube comprising an envelope, main electrodes in the envelope between which electric current passes, a firing electrode, and a gas in said envelope which is excited to light emission by the passage of said current, said emission including ultraviolet light, the improvement comprising: said envelope comprising a straight discharge duct and electrode chambers at the ends of the duct, each of said electrode chambers having a volume which is at least equal to that of the discharge duct, said main electrodes being positioned in the electrode chambers respectively and outside said duct in a manner permitting free communication of said gas between said duct and said electrode chambers, said envelope having means for preventing any decrease of ultraviolet transmissivity of the envelope due to the effect of flash discharges through said duct.
 9. In an electronic flash tube as defined in claim 8, wherein said preventing means comprises: said electrode chambers extending at right angles to said discharge duct, an elongated reflector having a cooling air duct at the exterior thereof, said electronic flash tube being positioned with its discharge duct within the reflector and outside the cooling air duct and with said electrode chambers extending into said cooling air duct, and means for providing a cooling air stream through said cooling air duct, whereby in operation said envelope is substantially heated to prevent any change of ultraviolet transmissivity of the envelope.
 10. In an electronic flash tube as defined in claim 8, wherein said preventing means comprises: said envelope consisting of synthetic quartz glass.
 11. In a flash lamp apparatus including a flash tube as set forth in claim 8, storage capacitor means for supplying said current, discharge circuit means including said storage capacitor means and said flash tube, and flash tube firing means connected to said firing electrode, the improvement comprising: said discharge circuit means having a resistance so low that the peak current of the discharge is defined substantially only by the flash tube.
 12. In an apparatus as set forth in claim 11 used to apply radiation to a surface, wherein said flash tube is positioned to apply the radiation therefrom to said surface, said apparatus including: infrared radiator means positioned so that the radiation therefrom is also applied to said surface along with said radiation from said flash tube, said radiator means comprising second circuit means including a second flash tube, and means connecting said second circuit means to said firing means to fire the second flash tube a given period of time before said first mentioned flash tube is fired, said given period of time being such that the maximum of the infrared radiation from said second flash tube coincides with the ultraviolet radiation from the first mentioned flash tube.
 13. In an apparatus as set forth in claim 12, wherein said preventing means comprises: said envelope consisting of synthetic quartz glass. 